Refrigeration & AC - ISRO Mechanical & Aerospace Subject-Wise PYQ Practice
Practice topic-wise Refrigeration & AC previous year questions for ISRO Mechanical & Aerospace with instant step-by-step solutions and formula breakdowns.
All ISRO Mechanical & Aerospace papers
6 questions.
Question 1
Year: 2015 | Topic: Refrigeration and Air Conditioning
A carnot cycle refrigerator operates between 250 K and 300 K. Its coefficient of performance is
Answer: B. 5.0
Explanation: For a Carnot cycle refrigerator operating between a lower temperature $T_L$ and a higher temperature $T_H$, the Coefficient of Performance (COP) is given by $COP = \frac{T_L}{T_H - T_L}$. Substituting $T_L = 250$ K and $T_H = 300$ K yields $COP = \frac{250}{300 - 250} = \frac{250}{50} = 5.0$.
Question 2
Year: 2016 | Topic: Refrigeration and Air Conditioning
The working temperatures in evaporator and condenser coils of a refrigerator are $-25^{\circ}C$ and $30^{\circ}C$ respectively. The COP of the refrigerator is 0.85 of the maximum COP for a power input of 2 kW. The refrigeration effect produced will be
- A. 7.6 kW
- B. 9 kW
- C. 10.2 kW
- D. 12 kW
Answer: A. 7.6 kW
Explanation: The lower temperature is $T_L = -25 + 273 = 248 K$ and the higher temperature is $T_H = 30 + 273 = 303 K$. The maximum Carnot COP is $\frac{T_L}{T_H - T_L} = \frac{248}{303 - 248} = \frac{248}{55}$. The actual COP is $0.85 \times \frac{248}{55}$. Since COP is the ratio of the refrigeration effect ($Q$) to the work input ($W$), we have $0.85 \times \frac{248}{55} = \frac{Q}{2}$. Solving for $Q$ yields approximately 7.6 kW.
Question 3
Year: 2016 | Topic: Refrigeration and Air Conditioning
If a certain mass of moist air in an air tight vessel is heated to a higher temperature, then
- A. Specific humidity of the air increases
- B. Specific humidity of the air decreases
- C. Relative humidity of the air increases
- D. Relative humidity of the air decreases
Answer: D. Relative humidity of the air decreases
Explanation: Specific humidity is the actual mass of water vapor present per kg of dry air, which remains constant since it is a sealed airtight vessel. However, as the temperature increases, the saturation pressure of water vapor (the capacity of the air to hold moisture) increases. Relative humidity is the ratio of actual vapor pressure to saturation vapor pressure. Since the denominator (capacity) increases while the numerator remains constant, the relative humidity decreases.
Question 4
Year: 2018 | Topic: Refrigeration and Air Conditioning
The heat removal rate from a refrigerated space is 7.2 kW and the power input to the compressor is 1.8 kW. The coefficient of performance (COP) of the refrigerator is
Answer: A. 4
Explanation: COP of refrigerator = Heat removed from space / Work done = 7.2 / 1.8 = 4.
Question 5
Year: 2024 | Topic: Refrigeration and Air Conditioning
What is the power of 2 tonne refrigeration system? Latent heat of ice may be taken as 336 kJ/kg and specific heat capacity of water as 4 kJ/kgK.
- A. 7.7 kW
- B. 70 kW
- C. 12.5 kW
- D. 0.7 kW
Answer: A. 7.7 kW
Explanation: One tonne of refrigeration is the rate of heat removal required to freeze 1000 kg (1 metric tonne) of water at 0 °C in 24 hours. Power for 1 Tonne = (1000 kg * 336 kJ/kg) / (24 * 3600 s) = 336,000 / 86,400 = 3.88 kW. For 2 tonnes, power = 2 * 3.88 = 7.77 kW, which approximates to 7.7 kW.
Question 6
Year: 2024 | Topic: Refrigeration and Air Conditioning
A Carnot refrigerator works in temperature range of 300 K to 270 K with different refrigerants CFC, R-32 and ammonia. Which of the refrigerant give better COP?
- A. CFC
- B. R-32
- C. Ammonia
- D. All gives same COP
Answer: D. All gives same COP
Explanation: The Coefficient of Performance (COP) of a Carnot refrigerator depends entirely on the absolute temperatures of the heat source and heat sink, and is completely independent of the properties of the working fluid (refrigerant) used.